CN101142637B - superconducting cable - Google Patents

Abstract

The present invention provides a superconducting cable with a further reduced cable diameter and a DC transmission system including the superconducting cable. A superconducting cable (1) has a structure in which two cable cores (2) are twisted together and accommodated in a heat insulating tube (8), each cable core having a superconducting Conductor layer (4) and outer superconducting layer (6). Each cable core (2) has a shaper (3), a superconducting conductor layer (4), an insulating layer (5), an outer superconducting layer (6) and a protective layer (7) in order from the center. In unipolar transmission, the superconducting conductor layers (4) of the two cores (2) are used as the outgoing line for carrying the unipolar current, and the outer superconducting layers (6) of the two cores (2) are used as the The return line for the return current. In bipolar transmission, the superconducting conductor layer (4) of one core (2) is used as the positive pole transmission, the superconducting conductor layer (4) of the other core (2) is used as the negative pole transmission, and the two cores ( The outer superconducting layer (6) of 2) is used as a neutral layer.

Description

superconducting cable

technical field

The present invention relates to a superconducting cable formed by twisting together a plurality of cable cores and a DC transmission system including the superconducting cable. In particular, the invention relates to superconducting cables whose diameter can be further reduced.

Background technique

As an AC superconducting cable, a known three-core twisted type cable is formed by twisting three cable cores together. Fig. 4 is a cross-sectional view of a three-core twisted type cable for three-phase AC. The superconducting cable 100 has a structure in which three cable cores 102 are twisted together and accommodated in a heat insulating tube 101 . The heat insulation pipe 101 has a double pipe structure composed of an outer pipe 101a and an inner pipe 101b between which a heat insulating material (not shown) is provided. The space between the outer tube 101a and the inner tube 101b is evacuated. On the outer periphery of the heat insulating pipe 101, a corrosion-resistant coating 104 is provided. Each cable core 102 includes a shaper 200 , a superconducting conductor layer 201 , an insulating layer 202 , a superconducting shielding layer 203 , and a protective layer 204 in order from the center. The void 103 is surrounded by the inner tube 101b, and the cable core 102 forms a channel for a coolant such as liquid nitrogen.

When AC transmission is performed by using the above-mentioned superconducting cable, not only the AC loss due to inductance is large but also the current at the time of short circuit is large, and the temperature may rise excessively due to the loss at that time. Compared with AC transmission, DC transmission using superconducting cables not only eliminates AC loss but also reduces short-circuit current. As a DC superconducting cable, Patent Document 1 has proposed a superconducting cable formed by twisting together three cable cores each having a superconducting conductor and an insulating layer. In this superconducting cable, individual cores are respectively used as a positive core, a negative core, and a neutral core for bipolar transmission.

Patent Document 1: Published Japanese Patent Application Tokukai 2003-249130.

Contents of the invention

The technical problem solved by the invention

In the superconducting cable disclosed in the aforementioned Patent Document 1, bipolar transmission is possible using a single cable. However, the cable provides not less than three cable cores in one cable, thereby increasing the cable diameter. Therefore, depending on the installation space, there is a possibility that the cable cannot be applied. Therefore, for DC transmission, it is desired to develop a superconducting cable that can further reduce the cable diameter. In addition, the AC superconducting cable shown in FIG. 4 also has three cores in one cable. Therefore, this cable has the same large cable diameter as the cable described in Patent Document 1 above.

In view of the foregoing, a main object of the present invention is to provide a superconducting cable having a smaller cable diameter. Another object of the present invention is to provide a superconducting cable suitable for DC transmission. Yet another object is to provide a DC transmission system comprising the above-mentioned superconducting cable.

way of solving the problem

The present invention achieves the above objects by reducing the number of cores in one cable.

More particularly, the superconducting cable of the present invention is characterized in that the cable is formed by twisting together two cable cores, each cable core having the following components:

(a) a superconducting conductor layer;

(b) an insulating layer provided on the outer periphery of the aforementioned superconducting conductor layer; and

(c) An outer superconducting layer provided on the outer periphery of the aforementioned insulating layer.

The DC transmission system of the present invention is a transmission system including the superconducting cable described above, and performs transmission by using a superconducting conductor layer and an outer superconducting layer provided in a core described below.

(unipolar transmission)

The superconducting conductor layer provided in both cores is used as the outbound line, and the outer superconducting layer provided in both cores is used as the return line.

(bipolar transmission)

A layer of superconducting conductors provided in one of the cores is used to transport one pole; either positive or negative. A layer of superconducting conductor provided in the other core is used for transport for the other pole. An outer superconducting layer provided in both cores is used as a neutral line.

In the above-mentioned AC superconducting cable shown in FIG. 4 and in the DC superconducting cable described in Patent Document 1, in order to obtain a shrinkage margin of the cable core at the time of cooling, the cable has three cores to provide slack. twisted structure. However, a structure having three cores in one cable cannot avoid an increase in cable diameter.

另外，通过在相邻的芯之间设置一个具有5mm厚度的隔离物来提供松弛部分时，包络圆的直径达到约83.3mm

For example, the following calculations are performed for a DC superconducting cable having a structure in which, starting from the center, each of the three cable cores has, in order, a former, a superconducting conductor layer, an insulating layer, a Formed shielding layer and protective layer. In this cable, individual cores are used as positive core, negative core and neutral core respectively. Assume that the superconducting conductor layer including the shaper has a diameter of 20 mm, the insulating layer has a thickness of 5 mm, the shielding layer has a thickness of 1 mm, and the protective layer has a thickness of 2 mm. Then, the diameter of the enveloping circle of the three cores reaches about 77.6mm

In addition, when the slack is provided by providing a spacer having a thickness of 5 mm between adjacent cores, the diameter of the envelope circle reaches about 83.3 mm

On the other hand, in a DC superconducting cable, when a shield layer formed of a superconducting material is used as an outer superconducting layer, and then the outer superconducting layer is used as a return line or a neutral layer, the number of cores can be is two. The two-core cable may have a smaller cable diameter than the above-mentioned superconducting cable with three cores. For example, as in the previous calculation, another calculation is performed below for a superconducting cable having a structure in which, starting from the center, each of the two cable cores has a shaper, a superconducting conductor layer, , insulating layer, outer superconducting layer and protective layer. In this cable, the superconducting conductor layers of the individual cores are used for the transmission of the positive and negative poles respectively, and the outer superconducting layers of the two cores are used as the neutral layer. Assume that the superconducting conductor layer including the shaper has a diameter of 20 mm, the insulating layer has a thickness of 5 mm, the outer superconducting layer has a thickness of 1 mm, and the protective layer has a thickness of 2 mm. Then, the diameter of the enveloping circle of the two cores reaches 72 mm ((20+5×2+1×2+2×2)×2=72). In addition, when the slack is provided by providing a spacer having a thickness of 5 mm between the cores, the envelope circle has a diameter of 77 mm (72+5=77). As described above, when a two-core structure is used, the cable diameter can be smaller than that of the above-mentioned superconducting cable having a structure in which three cable cores are twisted together.

Also for the AC superconducting cable, three-phase AC transmission can be performed by using a plurality of superconducting cables having two cable cores while reducing the cable diameter of one cable.

Therefore, the present invention specifies that the number of cores be two. The present invention will be explained in more detail below.

It is specified that the superconducting cable of the present invention is formed by twisting together two cable cores, each cable core having the following components:

(a) a superconducting conductor layer;

(b) an insulating layer provided on the outer periphery of the aforementioned superconducting conductor layer; and

(c) An outer superconducting layer provided on the outer periphery of the aforementioned insulating layer.

Especially, in the present invention, for unipolar transmission, the outer superconducting layer is used as a return line, and for bipolar transmission, the outer superconducting layer is used to circulate unbalanced or abnormal current between positive and negative electrodes. Therefore, the outer superconducting layer is formed by using a superconducting material.

It is proposed that the superconducting conductor layer be formed by helically winding a tape-type wire having a structure in which a plurality of filaments made of, for example, a Bi-2223-based superconducting material are placed in a matrix such as a silver sheath. The superconducting conductor layer may be a single layer or may be composed of multiple layers. When a multilayer structure is used, an insulating layer may be provided between layers constituting the superconducting layer. Between the constituent superconducting layers can be provided by spirally winding insulating paper such as kraft paper or semi-synthetic insulating paper such as PPLP (registered trademark, produced by Sumitomo Electric Industries, Ltd.) (PPLP is an abbreviation for polypropylene laminated paper) insulation layer. The above-mentioned superconducting conductor layer is formed by helically winding the aforementioned electric wire made of a superconducting material on the outer periphery of the former. The former may be a solid or a hollow body formed by using a metallic material such as copper or aluminum. For example, it may have a structure in which a plurality of copper wires are twisted. As the copper wire, an electric wire with an insulating coating can be used. The shaper serves as an element for maintaining the shape of the superconducting conductor layer. A buffer layer may be provided between the shaper and the superconducting conductor layer. The buffer layer avoids direct metallic contact between the shaper and the superconducting wire to prevent damage to the superconducting wire. In particular, the buffer layer may also be used to further smoothen the surface of the shaper when the shaper is formed from stranded wire. As a special material for the buffer layer, insulating paper or carbon paper can be used appropriately.

The insulating layer may be formed by spirally winding semi-synthetic insulating paper such as PPLP (registered trademark) or insulating paper such as kraft paper. The insulating layer is designed to have a dielectric strength required for insulation between the superconducting conductor layer and the ground.

When the superconducting cable of the present invention is used for DC transmission, the above-mentioned insulating layer may be configured to have p (resistivity) grading to level the radial (thickness direction) distribution of the DC electric field. The p-grading is performed such that the resistivity decreases as the radial position moves toward the innermost portion of the insulating layer, and increases as the radial position moves toward the outermost portion. Performing p grading changes the resistivity in terms of the thickness of the insulating layer stepwise. The ρ grading can flatten the distribution of the DC electric field in the thickness direction throughout the insulating layer. As a result, the insulation thickness can be reduced. Therefore, ρ grading is desirable because it further reduces the cable diameter. Each layer has a different resistivity, and the number of layers is not particularly limited. In practice, however, two or three layers or so are used. In particular, when the thicknesses of the layers are equal, smoothing of the DC electric field distribution can be effectively performed.

For p-grading, it is recommended to use insulating materials with different resistivities (p's). For example, when insulating paper such as kraft paper is used, the resistivity can be varied, for example, by changing the density of the kraft paper or by adding cyanoguanidine to the kraft paper. When using a composite paper composed of insulating paper and plastic film such as PPLP (registered trademark), the resistivity can be changed by changing the ratio k of the thickness tp of the plastic film of the composite paper to the total thickness T (ratio k, expressed as (tp/T )×100) or by changing the density, quality, additives, etc. of the insulating paper. Desirably, for example, the value of the ratio k is in the range of about 40% to 90%. Generally, as the ratio k increases, the resistivity ρ increases.

In addition, in the vicinity of the superconducting conductor layer, the insulating layer has a high ε (dielectric constant) layer, which has a higher dielectric constant than other parts, which not only improves the performance of withstanding DC voltage, but also improves the performance of withstanding pulse voltage. Performance is also improved. The values of the dielectric constant ε (at 20°C) are summarized as follows:

(a) Ordinary kraft paper: about 3.2 to 4.5

(b) Composite paper with ratio k of 40%: about 2.8

(c) Composite paper with ratio k of 60%: around 2.6

(d) Composite paper with ratio k of 80%: about 2.4.

In particular, it is desirable to form an insulating layer by using composite paper having a high ratio k and including kraft paper having relatively high airtightness, because such a structure is excellent in both DC and pulse withstand voltage.

In addition to the ρ grading described above, the insulating layer may be constructed such that the dielectric constant ε increases as the radial position moves toward the innermost part, and the dielectric constant ε increases as the radial position moves toward the outermost part. reduced. The ε grading can also be formed radially throughout the insulating layer. As described above, by performing ε classification, the superconducting cable of the present invention becomes a cable having excellent DC performance, making itself suitable for DC transmission. On the other hand, at present, most transmission lines are constructed as AC systems. Considering the transformation of the transmission system from AC to DC in the future, it is conceivable that before the transformation into DC transmission, there is still such a situation that AC transmission is performed by temporarily using the cable of the present invention. For example, there may be a case where, although part of the cable in the transmission line has been replaced with the superconducting cable of the present invention, the remaining part is constituted by the AC transmission cable. Another conceivable situation is one in which, although the AC transmission cable in the transmission line is replaced by the superconducting cable of the present invention, the power transmission device connected to the cable is still for AC use. In this case, first, AC transmission is temporarily performed using the cable of the present invention, and then, finally, a transition to DC transmission will be performed. Therefore, it is desired that the cable of the present invention not only has excellent DC performance but also be designed by considering AC performance. Also, when AC performance is considered, a cable having excellent performance against pulse voltage such as surge voltage can be constructed by using an insulating layer whose dielectric constant when moving toward the innermost part in its radial position ε increases and the permittivity ε decreases as its radial position moves towards the outermost part. Later, when the aforementioned transition period ends and DC transmission starts, the cable of the present invention used in the transition period can be used as a DC cable without any change. In other words, the cables of the invention constructed not only by ρ but also by ε are also suitable for use as AC/DC cables.

In general, the above-mentioned PPLP (registered trademark) has properties such that as the ratio k increases, the resistivity ρ increases and the dielectric constant ε decreases. Therefore, when the insulating layer is constructed in such a way that when moving toward the outermost part in the radial position, using PPLP (registered trademark) having a higher ratio k, the insulating layer can have such a property that in the radial direction As the position moves toward the outermost portion, the resistivity ρ increases, while at the same time the permittivity ε decreases.

On the other hand, kraft paper generally has properties such that as the airtightness increases, the resistivity ρ increases and the dielectric constant ε also increases. Therefore, when only kraft paper is used, it is difficult to construct the insulating layer in such a way that the resistivity ρ increases while the dielectric constant ε decreases as the radial position moves toward the outermost portion. Therefore, when using kraft paper, it is desirable to construct an insulating layer by combining it with composite paper. For example, it is suggested that a kraft paper layer is formed at the innermost part of the insulating layer, and a PPLP layer is formed at the outer side of the kraft paper. In this case, the PPLP layer has a higher resistivity p than the kraft paper layer, and at the same time, the PPLP layer has a lower dielectric constant ε than the kraft paper layer.

An outer superconducting layer is provided on the above-mentioned insulating layer. With the aforementioned superconducting conductor layer, the outer superconducting layer is formed by using a superconducting material. The superconducting material to be used for the outer superconducting layer may be similar to that used to form the aforementioned superconducting conductor layer. The outer superconducting layer is set at ground potential. When bipolar transmission is performed using the superconducting cable of the present invention, positive and negative currents generally have almost the same magnitude and cancel each other out. Therefore, almost no voltage is applied to the outer superconducting layer used as a neutral layer. However, when an imbalance occurs between the positive and negative electrodes, an unbalanced current flows through the outer superconducting layer. Also, when bipolar transmission is converted to unipolar transmission due to an anomaly in one pole, a current equivalent to the transmitted current flows through the outer superconducting layer because the outer superconducting layer is used as a return line for unipolar transmission. guide layer. In view of these circumstances, in the present invention, the outer superconducting layer is formed of a superconducting material. It is desirable that the protective layer also acts as an insulating layer provided on the outer periphery of the outer superconducting layer.

In addition, the semiconductor layer is formed on the inner circumference, the outer circumference, or both of the insulating layer. In particular, it may be formed between the superconducting conductor layer and the insulating layer, between the insulating layer and the outer superconducting layer, or both. Upon formation of the inner semiconducting layer, which is the former, or the outer semiconducting layer, which is the latter, the contact between the superconducting conductor layer or the outer superconducting layer and the insulating layer begins to increase. Therefore, destruction due to partial discharge or the like is suppressed.

Two cable cores having the above-mentioned structure were prepared. By twisting these two cores together, the superconducting cable of the present invention can have a structure that provides a margin for contraction when the cable is cooled. Since the structure provides a margin for shrinkage, that is, as a structure for absorbing the amount of heat shrinkage, for example, the core can be twisted by providing the core with slack. For example, the slack may be formed by stranding the cores together with spacers between the cores, then when the stranded cores are housed in a thermally insulating tube (or when a thermally insulating tube is formed on the stranded cores) Remove the spacer. The spacer may be formed from a piece of felt, for example having a thickness of about 5 mm. It is recommended to appropriately change the thickness of the spacer according to the diameter of the cable core.

The superconducting cable of the present invention is constructed by twisting the above-mentioned two cores together and housing the twisted body in a heat insulating tube. The heat insulating pipe may have a structure in which, for example, a double pipe structure consists of an outer pipe and an inner pipe, between which the heat insulating pipe material is placed, and the space between the outer pipe and the inner pipe is evacuated into vacuum. In the inner tube, the space surrounded by the outer surface of the cable core and the inner surface of the inner tube is filled with a coolant such as liquid nitrogen for cooling the cable core. The space is used as a passage for the coolant. An anti-corrosion coating is provided on the outer periphery of the heat insulating pipe by using a resin such as polyvinyl chloride.

It is desirable to have a structure in which the coolant channel in the inner tube of the above-mentioned thermally insulating tube is used as an external channel for the coolant, and a return channel for the coolant is provided separately, because such a structure reduces damage from intrusion. hot. As a coolant return channel, a coolant circulation pipe can be used. It is desirable to have a structure in which the coolant circulation pipe is twisted together with the two cores because it is easy to place the coolant circulation pipe in the thermal insulation pipe. In order not to increase the cable diameter by compressing the coolant circulation tube, the coolant circulation tube is designed such that it has a smaller diameter than the core so that the two cores and the enveloping circle of the coolant circulation tube can have the same diameter as the two cores The enveloping circle has the same diameter. The number of the above-mentioned coolant circulation pipes can be one or two or even more.

It is desirable that the aforementioned coolant circulation tube has expansion-contraction properties such that the tube contracts when the cable cools. Since the coolant circulation pipe has expansion-contraction properties, it is desirable to use, for example, a bellows made of a metal material such as stainless steel which has excellent strength even at the coolant temperature. When just two cores are twisted together, slack is required for shrinkage while the cable cools. However, when using a coolant circulation tube having an expansion-contraction property, the coolant circulation tube may be twisted together with two cores without providing a slack. The reason is that even when the slack cannot be ensured (when only two cores are twisted together, as described above, slack for contraction is required), the expansion-contraction performance of the coolant circulation tube itself can absorb the amount of contraction . In addition, a protective layer may be provided on the outer circumference of the coolant circulation pipe by spirally winding kraft paper or the like. By providing a protective layer, it is possible to prevent the coolant circulation pipe from coming into contact with the core or the heat insulating pipe. Therefore, their damage and other problems can be suppressed.

The superconducting cable of the present invention having the above structure can be used for unipolar transmission by using the following arrangement:

(a) a superconducting conductor layer provided in both cores is used as an outbound line; and

(b) The outer superconducting layer provided in both cores is used as a return line.

Alternatively, the cable can also be used for bipolar transmission by using the following arrangement:

(a) the layer of superconducting conductor provided in one of the cores is used for the transmission of one pole; the one pole being positive or negative;

(b) a superconductor layer provided in the other core is used for transmission at the other pole; and

(c) The outer superconductor layer provided in each core is used as a neutral line.

Also, during bipolar transmission, one pole may experience anomalies in the superconducting conductor layer for that pole or eg in the DC-AC converter connected to the cable. In this case, when the pole needs to stop power transmission due to abnormality, the cores for other intact poles can be used for unipolar transmission. In particular, the superconducting conductor layer of the core for an intact pole can be used as a forward line and the outer superconducting layer of the same core as a return line. In either transmission system, whether unipolar or bipolar, the outer superconductor layers of the two cores are set to ground potential.

The superconducting cable of the present invention is suitable for not only DC transmission but also AC transmission by providing an insulating layer structure having the ε-gradation as described above. When performing single-phase AC transmission, a superconducting cable of the present invention can be used. In this case, the superconducting conductor layer of each core can be used for phase power transmission, while the outer superconducting layer of each core is used as a shielding layer. Alternatively, the superconducting conductor layer of one core may be used for phase power transfer, the outer superconducting layer of the same core used as a shield, and the remaining core used as a spare. After being used for single-phase AC transmission, when the superconducting cable is used for DC transmission, the cable can be used for unipolar transmission or can be used for bipolar transmission. When performing three-phase AC transmission, two or three superconducting cables of the present invention are prepared so that the total number of cores becomes at least three. When two cables are used, the total number of cores becomes four. Therefore, it is proposed to use one core as a spare core, the superconducting conductor layers of the remaining three cores are used for the transmission of each phase, and the outer superconducting layer is used as a shielding layer. When using three cables, it is recommended that the superconducting conductor layer of each cable is used for the transmission of each phase and that the outer superconducting layer is used as a shielding layer. In other words, it is suggested that two cores are used for the transmission of one phase. When these superconducting cables are used for DC transmission after three-phase AC transmission, each cable can be used for unipolar transmission or bipolar transmission.

Invention effect

The superconducting cable of the present invention having the above structure also has a further reduced cable diameter. It is also possible to use one cable for bipolar transmission. In addition, even when an abnormality occurs in one of the poles, transmission can be performed by switching bipolar transmission to unipolar transmission. Also, the superconducting cable of the present invention has coolant circulation pipes without increasing the diameter of the cable. Such a structure can reduce the heat from intrusion.

In addition, in the core provided in the superconducting cable of the present invention, by performing ρ grading in the insulating layer, the distribution of the thickness direction of the DC electric field can be made even throughout the insulating layer. As a result, the performance of withstanding DC voltage is improved, and therefore, the thickness of the insulating layer can be reduced. Therefore, the cable diameter can be further reduced. In addition to p grading, by providing an insulating layer having a high ε near the superconducting conductor layer, the pulse voltage withstand performance can be improved in addition to the above-mentioned improvement of the DC voltage withstand performance. In particular, by configuring the insulating layer in such a way that ε increases as its radial position moves toward the innermost part and ε decreases as it moves in the radial position toward the outermost part, the present The invented superconducting cable can be a cable that also has excellent AC electrical properties. Therefore, the superconducting cable of the present invention is suitable not only for DC transmission and AC transmission but also for use during the transition of the transmission system between AC and DC.

best practice

Embodiments of the present invention are explained below.

Example 1

FIG. 1(A) is a schematic structural view showing a state in which a DC transmission line for unipolar transmission is constructed by using the superconducting cable of the present invention. FIG. 1(B) is a schematic cross-sectional view showing a state where spacers are provided between cable cores in a superconducting cable. In the following drawings, the same reference numerals denote the same elements. The superconducting cable 1 has a structure in which two cable cores 2 each having a superconducting conductor layer 4 and an outer layer made of a superconducting material are twisted together and housed in a heat insulating tube 8. superconducting layer6. Each cable core 2 has a shaper 3 , a superconducting conductor layer 4 , an insulating layer 5 , an outer superconducting layer 6 and a protective layer 7 in order from the center.

In this example, the superconducting conductor layer 4 and the outer superconducting layer 6 were formed by using a Bi-2223-based superconducting stripline (Ag-Mn-coated stripline). The superconducting conductor layer 4 is constituted by helically winding the aforementioned superconducting tape shaped wire on the outer periphery of the former 3 . The outer superconducting layer 6 is formed on the insulating layer 5 in the same manner as above. The shaper 3 is formed by twisting a plurality of copper wires. A buffer layer (not shown) made of insulating paper is formed between the former 3 and the superconducting conductor layer 4 . On the outer periphery of the superconducting conductor layer 4, the insulating layer 5 is constituted by spirally winding a semi-synthetic insulating paper (PPLP: registered trademark, produced by Sumitomo Electric Industries, Ltd.). The insulating layer 5 is provided so that the insulation between the superconducting conductor layer 4 and the ground has a required dielectric strength. A protective layer 7 is provided by spirally winding insulating paper on the outer periphery of the outer superconducting layer 6 .

In this example, two cable cores 2 are prepared, each having a shaper 3 , a superconducting conductor layer 4 , an insulating layer 5 , an outer superconducting layer 6 and a protective layer 7 . These two cable cores 2 are twisted together with slack so that there is a shrinkage margin required for thermal shrinkage, and the cable cores 2 are accommodated in the heat insulating tube 8 . In this example, the heat insulating pipe 8 is formed of a corrugated stainless steel pipe. Conventional superconducting cable as shown in Fig. 4, this thermal insulating tube 8 has the double-tube structure that is made up of outer tube 8a and inner tube 8b, between these two tubes, multiple layers of thermal insulating material (not shown) are placed. out). The space between the twin tubes is evacuated. Therefore, the thermal insulation pipe 8 has an evacuated multilayer thermal insulation structure. The interspace 9 surrounded by the inner tube 8b and the two cable cores 2 forms a passage for a coolant, for example liquid nitrogen. A corrosion-resistant coating (not shown) made of polyvinyl chloride is formed on the outer periphery of the heat insulating pipe 8 . In addition, these two cable cores 2 are twisted together and have a slack portion, which is accommodated in thermal insulation by placing a spacer 90 between the cores 2 as shown in FIG. 1(B) and then in the twisted body. This spacer 90 is removed while in the tube 8 (or at the same time as the heat insulating tube 8 is formed on the strand). In this example, the spacer 90 is formed from a sheet of felt having a thickness of 5 mm and having a rectangular cross-section.

The superconducting cable 1 of the present invention having the above structure can be used for DC transmission, more specifically bipolar transmission or unipolar transmission. First, the case where unipolar transmission is performed is explained. For unipolar transmission, it is recommended to construct a transmission line as shown in Figure 1(A). In particular, one end of the superconducting conductor layer 4 provided in the core 2 on the right side of FIG. Shows). The other end of the same superconducting conductor layer 4 is connected by a lead wire 22 to a DC-AC converter 11, which is connected to an AC system (not shown). Similarly, one end of superconducting conductor layer 4 provided in core 2 on the left side of FIG. 1(A) is connected to DC-AC converter 10 through lead wire 23 and lead wire 21 . The other end of the same superconducting conductor layer 4 is connected to the DC-AC converter 11 through a lead wire 22 . On the other hand, the outer superconducting layers 6 of the two cores 2 are connected to the DC-AC converter 10 through the leads 24 , 25 and 26 , and to the DC-AC converter 11 through the lead 27 . In this example, lead 26 is grounded. This grounding sets the outer superconducting layer 6 at ground potential. In this example, a single-ended ground is used. However, it is also possible to use both ends grounding by grounding the lead wire 27 . The leads 20 to 27 electrically connect the superconducting conductor layer 4 and the outer superconducting layer 6 using the DC-AC converters 10 and 11 .

By providing the superconducting conductor layer 4 in both cores 2 as the outgoing line carrying the unipolar current and by providing the outer superconducting layer 6 in the two cores 2 as the return line carrying the return current, there is The DC transmission line of the aforementioned structure can be used for unipolar transmission. In addition, a superconducting cable is formed by twisting the two cable cores together in such a way that a slack is formed. Therefore, the slack can absorb the amount of thermal contraction upon cooling. Also, the superconducting cable 1 has a smaller number of cores than conventional cables. Therefore, the cable can reduce the cable diameter.

Example 2

Next, the case where bipolar transmission is performed is explained. FIG. 2(A) is a schematic structural view showing the state of constructing a DC transmission line for bipolar transmission by using the superconducting cable of the present invention. (B) is a structural schematic diagram showing a state in which a DC transmission line for unipolar transmission is constructed by using a superconducting cable layer of one of the cores and an outer superconducting layer. The superconducting cable 1 used in Example 1 can also be used for bipolar transmission. For bipolar transmission, it is recommended to construct the transmission line as shown in Fig. 2(A). More specifically, one end of the superconducting conductor layer 4 provided in one of the cores 2 (the right core 2 in FIG. to the AC system (not shown). The other end of the same superconducting conductor layer 4 is connected via a lead wire 31 to a DC-AC converter 13, which is connected to an AC system (not shown). Similarly, one end of outer superconducting layer 6 provided in the same core 2 is connected to DC-AC converter 12 through lead wire 32 and lead wire 33 . The other end of the same outer superconducting layer 6 is connected to the DC-AC converter 13 by a lead wire 34 . On the other hand, one end of the superconducting conductor layer 4 provided in the other core 2 (the left core 2 in FIG. to the AC system (not shown). The other end of the same superconducting conductor layer 4 is connected via a lead wire 36 to a DC-AC converter 15, which is connected to an AC system (not shown). Similarly, one end of outer superconducting layer 6 provided in the same core 2 is connected to DC-AC converter 14 through lead wire 37 and lead wire 33 . The other end of the same outer superconducting layer 6 is connected to the DC-AC converter 15 by a lead wire 34 . Lead 33 is grounded. This grounding puts the outer superconducting layer 6 at ground potential. In this example, single-ended grounding is used by grounding lead 33 only. However, two-ended grounding can also be used by grounding the lead wire 34 . Lead wires 30 to 37 electrically connect superconducting conductor layer 4 and outer superconducting layer 6 using DC-AC converters 12 , 13 , 14 and 15 .

The above-mentioned structure constitutes a positive pole circuit in the positive direction, and the positive pole circuit consists of a DC-AC converter 13, a lead wire 31, the superconducting conductor layer 4 of the core 2 on the right side of Fig. 2 (A), a lead wire 30, a DC-AC converter 12, Lead wire 33 , lead wire 32 , outer superconducting layer 6 and lead wire 34 constitute. On the other hand, the structure also constitutes a negative circuit in the positive direction, and the negative circuit consists of a DC-AC converter 15, a lead wire 36, the superconducting conductor layer 4 of the core 2 on the left side of Fig. 2 (A), a lead wire 35, a DC- AC converter 14, lead wire 33, lead wire 37, outer superconducting layer 6 and lead wire 34 constitute. A positive or negative circuit shown in the above positive direction enables bipolar transmission. In this structure, the outer superconducting layers 6 of the two cores 2 are used not only as a neutral layer but also to circulate an unbalanced or abnormal current between positive and negative electrodes. In this example, in FIG. 2(A), the core on the right is used for the positive electrode, and the core on the left is used for the negative electrode. However, of course, the usage can be reversed.

Even if one of the poles stops power transmission using its superconducting conductor layer due to an abnormality in the superconducting conductor layer for that pole or in the DC-AC converter, by using the superconducting conductor layer for the intact pole it is possible for unipolar transmission. For example, in FIG. 2(A), when abnormal conditions occur in the left core 2, DC-AC converters 14 and 15, etc., that is, when the negative pole produces abnormal conditions, the transmission of the left core 2 in FIG. 2(A) is used. stopped. In this case, as shown in FIG. 2(B), a transmission line for unipolar transmission is formed by using another core 2 (in FIG. 2(A), right core 2). More specifically, unipolar transmission is possible by using the superconducting conductor layer 4 of the core 2 as a forward line and the outer superconducting layer 6 of the same core as a return line. In this example, a case where an abnormality occurs in the negative electrode is explained. However, similar measures are also taken when an abnormality occurs in the positive electrode. In this case, by using the superconducting conductor layer 4 of the other core 2 (in FIG. The line is capable of unipolar transmission.

As explained above, the superconducting cable of the present invention can be used for bipolar transmission and monopolar transmission by using one cable. In particular, it is specified that the number of cable cores to have in one cable is two. Therefore, the cable diameter can be further reduced compared to a structure with three cores.

As previously described, for DC transmission, the insulating layer 5 is graded by p such that the resistivity decreases when moving towards the innermost part of the insulating layer in a radial position, while towards the outermost part in a radial position When the part moves, the resistivity increases, which can make the distribution of the DC electric field flat in the thickness direction in the insulating layer. Therefore, the thickness of the insulating layer can be further reduced. The resistivity can be varied by using different sets of PPLP (registered trademark), each with a different ratio k. As the ratio k increases, the resistivity tends to increase. In addition, when the insulating layer 5 is provided with a high ε layer in the vicinity of the superconducting conductor layer 4, the pulse voltage withstand performance can be improved in addition to the DC voltage withstand performance. The high ε layer can be formed, for example, by using PPLP (registered trademark) having a low ratio k. In this case, the high ε layers become low ρ layers. Also, in addition to the above-mentioned ρ grading, when the insulating layer 5 is formed in such a manner that the dielectric constant ε increases as it moves toward the innermost part in the radial position, while moving toward the outermost part in the radial position When moving, the dielectric constant ε decreases, and the insulating layer also has excellent AC performance. Therefore, the superconducting cable 1 is also suitable for AC transmission. For example, by using different groups of PPLP (registered trademark), each different group has a different ratio k. As follows, the insulating layer may be formed to have three different levels of resistivity and dielectric constant. It is recommended that the following three layers be set up in the following order from inside to outside (each X and Y represent a constant):

Low ρ layer: ratio (k): 60%, resistivity (ρ) (20°C): XΩ cm, dielectric constant (ε): Y;

Middle ρ layer: ratio (k): 70%, resistivity (ρ) (20°C): about 1.2XΩ·cm, dielectric constant (ε): about 0.95Y; and

High ρ layer: Ratio (k): 80%, resistivity (ρ) (20°C): about 1.4XΩ·cm, dielectric constant (ε): about 0.9Y.

When using superconducting cables 1 for three-phase AC transmission, it is recommended to use two or three superconducting cables 1 . When using two cables 1, it is recommended that among the four cores 2 of the two cables 1, one core 2 is used as a spare core, and the superconducting conductor layer 4 of the remaining three cores 2 is used for the transmission of each phase , while the outer superconducting layers 6 of the three cores 2 are used as shielding layers. When using three cables 1 , individual cables 1 are used for the transmission of the individual phases. More specifically, two cores 2 provided in each cable 1 are used for transmission of one phase. In this case, the superconducting conductor layers 4 of the two cores 2 provided in each cable 1 are used for the transmission of the respective phases, the outer superconducting layers 6 provided at the outside of these superconducting conductor layers 4 used as a shield. When the superconducting cable 1 is used for single-phase AC transmission, it is recommended to prepare a superconducting cable 1 using the superconducting conductor layers 4 of the respective cores 2 for transmission of the same phase, and to place the superconducting layers 4 on the outside The outer superconducting layer 6 is provided as a shielding layer.

After being used for the above-mentioned AC transmission, the superconducting cable 1 can be used for DC transmission, such as the above-mentioned unipolar transmission and bipolar transmission. As described above, the superconducting cable of the present invention having an insulating layer composed of p-classification and epsilon-classification is suitable for use as a DC/AC cable. The references to the p-scaling and epsilon-scaling are also applied in Example 3 below.

Example 3

Next, an explanation is given of a structure provided with both the coolant external passage and the coolant return passage. Fig. 3 shows a schematic cross-sectional view of a superconducting cable of the present invention, which is formed by twisting two cable cores and a coolant circulation tube together. In the above-mentioned Examples 1 and 2, an explanation was given of the structure in which the inner side of the inner pipe of the heat insulating pipe is used as the coolant passage. However, as shown in FIG. 3, the coolant circulation pipe 40 may be provided separately so that the void 9 in the inner pipe can be used as an external passage of the coolant so that the inside of the coolant circulation pipe 40 can be used as a return flow of the coolant. aisle. When the external passage and the return passage of the coolant are provided as described above, the intrusion of heat can be reduced.

In this example, two coolant circulation pipes 40 are prepared to form a structure in which two cable cores 2 and two coolant circulation pipes 40 are twisted together. In particular, in this example, a corrugated tube made of stainless steel is used as the coolant circulation tube 40 . When flexible pipes such as corrugated pipes are used, the expansion-contraction property of the coolant circulation pipe itself can absorb the amount of contraction when the cable is cooled. Therefore, when twisted together with the two cable cores 2, the coolant circulation pipe 40 is twisted so as not to form the aforementioned slack for contraction.

The coolant circulation pipe 40 is designed to have a smaller diameter than the cable core 2 . In addition, as shown in FIG. 3 , the enveloping circles of the two coolant circulation pipes 40 and the two cores 2 (circles drawn with dotted lines in FIG. 3 ) are designed to have the same diameter of. Therefore, even when the coolant circulation pipe 40 is provided in addition to the two cable cores 2, the superconducting cable has a cable diameter not larger than that shown in Examples 1 and 2 without the coolant circulation pipe 40. 1 diameter. In this example, two coolant circulation pipes 40 are used. However, the number of coolant circulation pipes may be one or three or even more. However, the size of the coolant circulation pipe must be chosen such that the enveloping circle of the coolant circulation pipe or pipes and the two cable cores can have the same diameter as the enveloping circle of the two cores.

Industrial Applicability

The superconducting cable of the present invention is suitable for use in electric lines for power transmission. In particular, the superconducting cable of the present invention is suitable not only for a device for transmitting DC power but also for a device for transmitting AC power during the transition period of converting the transmission system from AC to DC. Also, it is suitable to perform the DC transmission system of the present invention while performing DC transmission by using the superconducting cable of the present invention described above.

Description of drawings

Fig. 1 (A) is a structural schematic diagram showing the state of constructing a DC transmission line by using the superconducting cable of the present invention, (B) is a cross-sectional schematic diagram showing a superconducting cable arranged between cable cores The state of the isolate.

What Fig. 2 (A) shows is to construct the state of the DC transmission line for bipolar transmission by using the superconducting cable of the present invention, (B) shows the superconducting conductor by using one of the cores Layer and outer superconducting layer to construct a state-of-the-art DC transmission line for unipolar transmission.

Fig. 3 shows a schematic cross-sectional view of a superconducting cable of the present invention, which is formed by twisting two cable cores and a coolant circulation tube together.

Fig. 4 is a cross-sectional view of a three-core twisted type superconducting cable for three-phase AC.

Explanation of reference signs

1: superconducting cable; 2: cable core; 3: former; 4: superconducting conductor layer; 5: insulating layer; 6: outer superconducting layer; 7: protective layer; 8: thermal insulation tube; 8a: outer tube ;8b: Inner tube; 9: Gap; 10-15: DC-AC converter; 20-27, 30-37: Lead wire; 40: Coolant circulation tube; 90: Spacer; Conductive cable; 101: thermal insulation tube; 101a: outer tube; 101b: inner tube; 102: cable core; 103: void; 104: anti-corrosion coating; 200: former; 201: superconducting conductor layer; 202: Insulation layer; 203: superconducting shielding layer; 204: protective layer.

Claims (9)

1. A superconducting cable formed by twisting together a plurality of cable cores, each having: (a) a superconducting conductor layer; (b) an insulating layer provided on the outer periphery of the superconducting conductor layer; and (c) an outer superconducting layer provided on the outer periphery of the insulating layer; where the number of cable cores is two, and Wherein, in order to flatten the radial distribution of the DC electric field in the insulating layer, the insulating layer is structured by using p-grading such that the resistivity decreases as the radial position moves toward the innermost part of the insulating layer, while Moving toward the position towards the outermost part, the resistivity increases. 2. The superconducting cable according to claim 1, which has a two-core twisted structure with a margin for contraction when the cable is cooled. 3. The superconducting cable according to claim 1, which has a structure in which two cores and at least one coolant circulation tube are twisted together; the at least one coolant circulation tube has a smaller diameter than the core; The enveloping circle of the two cores and the at least one coolant circulation tube has the same diameter as the enveloping circle of the two cores. 4. The superconducting cable of claim 3, wherein said at least one coolant circulation tube: (a) having expansion-contraction properties such that said at least one coolant circulation tube can contract when the cable cools; and (b) Twisted with the two cores in such a way that no slack is formed for contraction when the cable cools. 5. The superconducting cable according to claim 4, wherein said at least one coolant circulation tube is a corrugated metal tube. 6. The superconducting cable according to claim 1, wherein, in the vicinity of the superconducting conductor layer, the insulating layer has a high ε layer having a higher dielectric constant than other portions. 7. The superconducting cable according to claim 1, wherein the insulating layer is constructed such that the dielectric constant ε increases as its radial position moves toward the innermost part, and the dielectric constant ε increases as the radial position moves toward the outermost part. The part moves, and the permittivity ε decreases. 8. A DC transmission system comprising the superconducting cable according to any one of claims 1-7, the DC transmission system performs unipolar transmission by the following method: (a) using a superconducting conductor layer provided in both cores as an outbound line; and (b) Using the outer superconducting layer provided in both cores as a return line. 9. A DC transmission system comprising the superconducting cable according to any one of claims 1-7, the DC transmission system performs bipolar transmission by the following method: (a) using a superconducting conductor layer provided in one of the two cores to perform transmission for one pole selected from the group consisting of positive and negative poles; (b) using a layer of superconducting conductor provided in the other core to provide transport for the other pole; and (c) Using the outer superconducting layer provided in both cores as a neutral line layer.

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